Computer information technology continues to spread expeditiously throughout our contemporary society. Moreover, the proliferation of such technology fuels a persistent demand for smaller and higher density storage devices. At present, computer technologies pervade many aspects of modern life in the form of portable devices such as PDA's, phones, pagers, digital cameras, MP3 players, and laptop computers to name but a few. Furthermore, the public's fervent desire for omnipresent computing technologies ensures that the movement toward developing small, fast, low power, inexpensive, and high-density memory will continue into the distant future. However, to meet such demand and make effective use of exponentially increasing processing power requires that novel data storage technologies be developed.
Memory technologies such as dynamic random access memory (DRAM) and synchronous random access memory (SRAM) are problematic at least because of the fact that they are volatile memory devices. While, volatile memory is important to computing devices, it is fundamentally more important to portable devices that information be capable of being stored without fear of loss due to a power failure (e.g. dead battery). Nevertheless, conventional nonvolatile mass storage devices are encountering inherent physical limitations that will restrict their growth and thus their usefulness in the future.
Magnetic storage devices are restricted in that their densities are constrained by superparamagnetism. Superparamagnetism is a phenomenon exhibited when the magnetic orientation energy, which holds the value of bits, equals the surrounding thermal energy of the disk device itself. In such a case, memory cells are caused to spontaneously flip at normal operating temperatures and previously stored data is jumbled. Therefore, magnetic storage technologies are limited in the amount of bits of information per square inch that they can store before thermodynamic effects compromise the data. Furthermore, the large size of conventional magnetic storage devices, such as computer hard drives, prohibits their successful use in small portable devices such as PDA's, mobile phones, and digital cameras.
Optical memory is also physically limited, not by superparamagnetism, but by the diffraction limit. Data is stored on an optical media in the form of pits of varying length formed by a laser beam. The size each recorded optical bit or spot size is limited by the wavelength of the light used to record each bit of information. In general, a smaller wavelength means a smaller spot size and a higher recording density. For example, typical compact disk (CD) uses a laser at a wavelength of 780 nm, which results in a spot size of about 1 micron, whereas, a digital versatile disk (DVD) operates at a wavelength of 650 nm resulting in a spot size of about 0.5 microns. Moreover, even though optical devices are capable of performing the same tasks as magnetic memory devices, they have inferior data rate and access times in addition to having a higher cost per megabyte.
Flash memory is a newer technology. Flash memory is solid-state storage technology, which provides such benefits as fast access times and small size. However, this technology is cost prohibitive with respect to mass storage. Specifically, the cost per megabyte of flash memory is extremely expensive when compared to other devices. For example, an 80-gigabyte hard drive currently costs under $200 (less than a quarter of a cent per MB), whereas 512-MB compact flash card costs around $230 (about 45 cents per MB). Accordingly, 80 gigabytes of flash memory would cost over $34,000. Thus, there is need for a new technology that is capable of storing a large amount of data, in a very small space, at a relatively low cost.